This file was created by scanning the printed publication.
Errors identified by the software have been corrected;
however, some errors may remain.
VARIABILITY AND DYNAMICS OF
SPOTTED OWL NESTING HABITAT
IN EASTERN WASHINGTON
Richard Everett
Sandra Martin
Monte Bickford
Richard Schellhaas
Eric Forsman
ABSTRACT
Corvallis, OR. Dr. Forsman is using radio telemetry to document habitat use and home range of six pairs of spotted
owls on the Wenatchee National Forest. This project is
part of the Spotted Owl RD&A Program under the direction of Kent Mays and his staff, Pacific Northwest Research
Station headquarters, Portland, OR.
This preliminary study documented the array of stand
conditions associated with six spotted owl nest sites, the character of the neighboring stands, and the disturbance regimes
that created current forest structure. Forest structure and
cover varied greatly among nest sites and the "neighborhood"
stands, but there are areas of commonality in the presence
of dense (>70% cover), multilayered canopies, and the presence of Douglas-fir and mistletoe brooms. Silvicultural prescriptions are suggested for the preservation of the spotted
owl and associated ecosystems. These prescriptions attempt
to mimic the intensity and frequency of processes that have
created the current spotted owl habitat.
SAMPLING FOREST STRUCTURE
AND COMPOSITION
The six nest sites occur on the Cle Elum Ranger District,
Wenatchee National Forest, in eastern Washington. Five
of the six sites supported reproductively successful pairs of
spotted owls during the 1989 nesting season. The sixth site
was used in 1990, but the nesting attempt was unsuccessful.
INTRODUCTION
Nest Stand
The Wenatchee Forestry Sciences Laboratory and the
Wenatchee National Forest have formed an integrated
RD&A team to work on the development of forest management practices which create or maintain spotted owl habitat. It is our belief that, through the creation of additional
or enhanced spotted owl habitat, we will be able to better
preserve the owl and retain timber harvest options.
Our approach is to build a biologically sound foundation
for the development of silvicultural prescriptions. This will
be achieved by (1) defining the current forest structure of
nest stands and adjacent neighborhood stands occupied by
reproductively successful spotted owl pairs, (2) examining
past formative events-natural and human induced-that
created the current spotted owl habitat, and (3) developing
silvicultural prescriptions that maintain desirable habitat
components or create new spotted owl habitat where it currently does not exist.
This paper reports on our initial study of six spotted owl
nest sites in the eastern Cascades in a coordinated project
with Dr . Eric Forsman, Pacific Northwest Research Station,
At each nest site, a l/lO-acre circular plot was centered
on the nest tree. All trees greater than 4.5 ft in height,
and with DBH ~ 1 in. were recorded for species, DBH, and
height. Age was determined for trees with DBH > 2 in.
Species, diameter, length, and decay stage were recorded
for each stump and log. Crown closure was measured with
a densimeter.
A l-chain-wide transect was placed in the nest tree stand
and a search made for evidence oflogging, road building,
and fire. Forest Service documentation of logging history
and onsite data collection were used to ascertain the logging histories of these sites. Increment borer tree cores or
wedges were taken from six to eight trees, snags, or stumps
having fire or logging damage scars to date time of disturbance (Arno and Sneck 1977).
Spotted Owl Neighborhoods
Nest stands are part of a patchwork of diverse forest communities across the landscape that make up the home range
of the spotted owl. Owl telemetry location points provided
by Dr. Forsman showed that approximately 90% of the owl
observations during the 1989 breeding season could be captured in a 1,000- to 1,200-acre area surrounding the nest
stand. We defined this portion of the home range around
the nest site as the "neighborhood."
Paper presented at the National Silviculture Workshop, Cedar City, UT,
May 6-9, 1991.
Richard Everett is Science Team Leader; Sandra Martin is Research
Wildlife Biologist, Pacific Northwest Research Station, Wenatchee, WA;
Monte Bickford is Silviculturist; Richard Schellhaas is a Forester,
Wenatchee National Forest, Wenatchee, WA; Eric Forsman is a Wildlife
Biologist, Pacific Northwest Research Station, Corvallis, OR.
35
Previous research on spotted owl ecology has shown that
owls prefer older, denser stands, they avoid clearcuts, and
are neutral to intermediate stand conditions (Carey and others 1990). Stand polygons within the neighborhood were
identified by < or > 40% cover, single- or multiple-canopy
layer, and the presence of trees >11 in. DBH. Stand types
were delineated within four of the six spotted owl neighborhoods on 1986 aerial photographs (Scale 1112000). Stands
do not meet the current definition for live tree "old growth"
because of the scarcity of trees greater than 30 in. in diameter (U.s. Department of Agriculture 1986). Our closest approximation to old-growth stands is that portion of Class 8
with greater than 70% crown canopy.
Table 1-Stand characteristics at six spotted owl nest sites on the
Wenatchee National Forest, WA
Site
Porky Basin
Hurley Creek
Ba~(er/Mill
Snow/Boulder
Taneum"
Gooseberry
Avg. all sites
Trees in the 60- to 100-year age classes were most numerous, but numbers varied greatly among sites (fig. 1). The
distribution of numbers of trees in each 2-in.-diameter class
similarly varied among sites (fig. 2). When trees ~20 in. are
totaled on the plots, we find 0, 1,2,3,4, and 9 trees in this
(years)
Maximum II of tr••• p.r plot
80,-----------~~----------------------~
60 ............................
. .............................................................. .
40 ............................
. .................................................................... .
30 ........................... .
20
10
O~~--~~--LJ-c~~L-~~~~~~~~~
80
80 100 12(; 140 180 180 200 220 240 280 280 380
Age Classes
Data from 8 .it••
_Max
1110 u
--Mean
plol (Ir . . . , 4.1i II I.")
Figure 1-Age class distribution for trees
located adjacent to the nest site.
8 10 12 14 18 18 20 22 24 28 28 3032 34 38 3840 42
Diameter Classes
Pine
_
Douglas-fir
Percent
Ft2/acre
Ft1
In.
92
93
95
93
95
88
93
190
200
250
210
270
200
220
23
30
38
53
67
29
3.9
44
4.8
7.2
8.1
10.1
5.9
6.7
Our preliminary study of nest sites showed that repeated
fires occurred in these stands. Fire occurrence averaged
13 years prior to 1900 (fig. 3). After 1900, fire frequency
increased to 18 to 20 years ontwo sites, and no fire scars
were found on the remaining sites. Prior to fire suppression, the ground fires appeared to maintain an open forest
on the sites (fig. 4). After fire suppression was initiated in
the early 1900's, rapid stand development occurred.
Logging replaced fires as the primary disturbance some
60 years ago. Stands without fire disturbance have gotten
denser, accumulated large amounts of biomass, and developed a dense tree understory of primarily grand fir (fig. 2).
Fires that occur in stands with heavy fuel loads on the
Wenatchee National Forest are now stand-destruction fires
that can cover 50,000 to 200,000 acres and which have destroyed spotted owl habitat.
In the 1970's, heavy western spruce budworm defoliation
hit the Forest. Although aerial spraying reduced budworm
populations to endemic low levels, the long-term solution
100
E222l Ponderosa
Average
diameter
DISTURBANCE REGIMES
Percent of all trees by diameter cia..
2 4 6
Average
height
size class among sites. The average tree diameter for the
sites is low (6.7 in.), but this is influenced by the high percentage of the trees in sapling and pole-size classes (table 1).
When these trees are removed from the calculations, the
average tree diameter more than doubles for all sites.
Height exhibited even greater variability among the
sites. The range of heights was greatest in the lower
height classes, but some variability was also found in midlevel classes. Average height for only those trees ~6 in.
DBH was roughly double that found for all trees on the
site ~4.5 ft tall.
Maximum age on the sites showed a wide range, from
128 to 368 years. The average age for trees ~6 in. DBH
was roughly 50% greater than for all trees ~4.5 ft tall.
Species composition did not vary greatly among the sites.
Grand fir dominated, but Douglas-fir was always present
and usually represented in the larger, older classes of trees
(fig. 2).
Total basal area, and particularly crown density, did not
exhibit the variability found with the other stand characteristics. Crown density was highly consistent, and considering the range of tree diameters and heights at these six
sites, this consistency is notable.
Tree Age
40
Total
basal area
lAverage from all trees >4.5 ft tall on a lho-acre circular plot, centered on
nest tree.
NEST STAND FINDINGS
20
Crown
density
~ Grand fir
Figure 2-Distribution of all trees by species
and diameter class adjacent to the nest stand.
36
SPOTTED OWL NEST STANDS
CV values for other habitat classes suggest that at least a
portion (26 to 36%) of the neighborhood is currently very
heterogeneous in cover and stand structure.
FIRE FREQUENCY (13 YR. AV. PRE 1900 )
ON YEARS)
VRS
DEVELOPING SILVICULTURAL
PRESCRIPTIONS FOR NON·HCA
AREAS
2a~----------------------------------
20
20
-.-.- .... ----.-.- - .......................... -.- .. --.-- .......... -....... ·18-···-·
.. 1A_ ................................. _.•• _•...... _.......••••.
12
11
16
10
Based on our preliminary information on current stand
and neighborhood characteristics and the knowledge of
how these stands developed, the Wenatchee National Forest proposes to use tree harvest to create and maintain owl
habitat as required. The Forest is also required to follow
the 1976 National Forest Management Act (U.S. Department of Agriculture 1983) that states "all forested lands in
the National Forest System shall be maintained in appropriate forest cover with species of trees, degree of stocking,
rates of growth, and condition of stands designed to secure
the maximum benefits of multiple-use sustained yield management in accordance with land management plans."
The Wenatchee National Forest developed a broad
landscape-level philosophy, "diversified age" management,
to maintain the landscape-level legacy of past harvest and
fire regimes. This management philosophy specifies a wide
range of silvicultural cutting methods to produce and maintain diversity of tree species and stand types. Selective
timber harvest scenarios to preserve the integrity of the
neighborhood and the mosaic of stand types is preferable
to custodial management where fuels buildup may lead to
large stand replacement fires.
A silvicultural prescription, "full stocking control," has
been developed for forest situations dominated by a mosaic
of small stands. The key ingredient is reduction of overstocking by removing those trees least likely to survive and
grow at acceptable rates. Emphasis is also on maintaining
or increasing the fire-tolerant species, especially ponderosa
pine, western larch, and Douglas-fir. Maintaining Douglasfir may be critical to providing spotted owl habitat as all
spotted owl nest sites on the Wenatchee National Forest
occur where at least some Douglas-fir is present. Without
the removal of a significant portion of canopy, Douglas-fir
is likely to be replaced by more shade-tolerant grand fir
(fig. 2).
The Wenatchee Forest Plan recognizes this problem and
prescribes an "extended shelterwood" system for managing
spotted owl habitat. This system uses a 130-year rotation,
leaving approximately 20 trees per acre until age 260 years.
This prescription will maintain stand productivity, reduce
wildfire hazard, and retain components of "old growth" forest. This prescription also provides for dispersal cover for
owls as recommended by the 50-11-40 rule of the Interagency Scientific Committee Report (Thomas and others
1990). Where spotted owl habitat exists, the report recommends that 50% of the area be in stands with trees greater
than 11 in. DBH and with 40% crown cover. Prescribed
tree removal from spotted owl habitat may be required
to safeguard these sites from wildfire that would degrade
stands to below the 50-11-40 rule.
The occurrence of mistletoe may increase silviculture
options if mistletoe brooms provide spotted owls with platforms required for nesting and raising young. Platforms
5 --;--···_·Y/1
HURLEY
PORKY
1_
PRE
BAKER
SNOW
f2Zj 190G-19DO
1iOO
GOOSE
I
PORKY.SAKER,aNOW (NO FIRE!! AFTER '1001
Figure 3-Fire frequency in five spotted
owl nest stands.
HURLEY CREEK
TREE AGE AND FIRE HISTORY
TREES I ACRE
70r-------------------------------------~
60
--- .... --.----.--.- _.----.---- ... «e- ... -- .. --..... -------- -.. --.-.
F
F
F
FFF
F
F
F
F
50
40
L L
L
50
LOGGING
100
150
L
YEARS BEFORE 1990
I
~ TREES PER AGE CLASS
200
250
I
F
FIRES
'(10 ye.r .ge cl .....1
Figure 4-Tree age and fire history on a
spotted owl nest site.
was to restore earlier successional species through regeneration cutting. The combination of fire, insect damage,
logging, and irregular topography has created a diverse
mosaic of stand conditions in spotted owl neighborhoods
on the Wenatchee National Forest.
NEIGHBORHOOD ANALYSIS
Spotted owl neighborhoods are a complex array of stand
types (fig. 5). Using the eight potential owl habitat classes,
the mean number of polygons was 42 (SD = 8) with an average size of31 acres (SD = 10). A majority of the acreage
(mean =858 acres, SD =86) is in Class 8 habitat, with
multilayered canopy, trees >11 in. dia., and greater than
40% canopy cover. Other habitat classes combined had
less total acreage (mean = 69 acres, SD = 56) and these
were divided among a greater number of polygons. The
coefficient of variation (CV) for acreages of specific owl
habitat classes among the neighborhoods varied from 6 to
178%. At 6%, habitat Class 8 had the lowest CV. The high
37
HABITAT
_
<40X SWALL SINGLE
CIJ <40X
lIT]]
SNALL NULTI
<40" LARGE SINGLE
rnm <40X LARGE NUL TI
o
>40" SMALL SINGLE
_
>40" SNALL MULTI
111>40" LARGE SINGLE
~>40" LAR.GE NULTI
Figure 5-Habitat polygons for four spotted owl neighborhoods. Polygons were classified by < or > 40% canopy cover, small vs. large trees « or > 11 in. DBH), and single
vs. multiple canopy layers. Neighborhoods are 1,000 to 1,200 acres in size.
suggests some flexibility in creating owl habitat in the eastern Cascades. The following prescriptions are adapted to
eastside forest conditions and are consistent with the
Committee's generalized silviculture treatments for manipulating forest structure.
Shelterwood cuttings, leaving an average of 20 of the
largest full-crowned trees, is a preferred regeneration method. This will create a two-storied stand similar to what we
found at nest sites we examined in this study. In stands
where Douglas-fir is present, the target should be at least
six trees per acre of this species. Residue removal levels
need to be moderate to provide sufficient down woody material as habitat for prey species, but not enough to create
an excessive fire risk. Desired fuel loading should be in
the range of 10 to 30 tons per acre.
Intermediate harvests that remove only the annual accumulation of biomass and maintain multilayered canopy
conditions are recommended. This would allow remaining
trees to more rapidly reach larger diameter classes. For
example, if we entered on a 15- to 20-year interval, and
our stands are growing 60 cubic feet per year/acre, we
can occur in large, defective trees with cavities or broken
tops or trees of an array of sizes that contain large mistletoe brooms. Our nest site studies have shown that spotted
owls will nest in mistletoe brooms in trees as small as 12 in.
DBR. Owls have successfully nested in stands with few
large trees when mistletoe brooms were present; however,
the long-term impacts of different nesting conditions on
spotted owl reproductive success are not yet known. Management for mistletoe brooms may allow for the more rapid
creation of components of owl habitat in younger and
smaller trees than in stands without mistletoe.
RECOMMENDED SILVICULTURAL
TREATMENTS
The Interagency Scientific Committee Report (Thomas
and others 1990) recommended several silvicultural approaches for mitigating harvest impacts on current and future owl habitat. The wide array in tree sizes present at
the nest sites (fig. 6) and mosaic of neighborhood stands
38
SPOTTED OWL NEST SITES
scenario for spotted owl habitat appears appropriate, but
rather we found an array of nest stand and neighborhood
conditions associated with six pairs of owls. From our preliminary investigation, we can conclude that spotted owl
habitat at these six sites is variable in stand structure under the canopy, but that canopy cover is consistently high,
and that stand composition is also fairly consistent. Much
of the spotted owl neighborhood does not meet the currently
accepted criteria of old growth, but a majority of stands had
multilayered canopy, greater than 70% crown cover, and
had trees >11 in. DBH present.
The neighborhood and surrounding landscape provide a
mix of contiguous, dense, multilayered stands and highly
diverse, small polygons. We hypothesize this mix of stands
meets the requirements of the owl and provides the habitat
necessary to support a variety of prey species throughout
the year. Although the neighborhoods we examined were
selected by nesting owls, the ultimate measure of habitat
quality must be the ability of the landscape to support a
portion of a viable population. Investigating the long-tenn
quality of forest neighborhoods surrounding spotted owl
nests in eastern Washington will require a minimum of
5 to 6 years of demographic data on resident owls.
The amount of variation in stand types within neighborhoods suggests many silvicultural treatments may be possible and perhaps required to maintain stand diversity.
Silviculture may provide an opportunity to improve stand
structure for owl habitat more rapidly than would occur by
natural processes alone.
The forest is dynamic; current nest stand and neighborhood characteristics are the result of past natural and
human-induced disturbances. Further changes in current
spotted owl nest stands and neighborhoods can be anticipated with or without the application of future silvicultural
prescriptions. We believe that the full range of potential
silvicultural options-from no intervention in natural succession to clearcutting of specific stands-will have a role
in perpetuating northern spotted owl habitat in eastern
Washington forests.
TREES) 11- DIA.
TREEIAC
HURLEY
PORKY
BAKER
8NOW
GOOSE
l7\NEUM
_NEST 8'QND
A
/tIf!...
ea
TRI!!lAC. [RANCII! ,.-111)
SPOTTED OWL NEST SITES
TREES ) 21- DIA.
TREE/AC
HURLEY
PORKY
BAKER
SNOW
GOOSE
l»oIEUM
_NEST STAND
B
/tIf!... , . TIU!!lAC. [RANGI! 1t-3U
Figure 6-Numbers of trees greater than 11 and
21 in. DBH at each nest site.
could remove 900 to 1,200 cubic feet. This approximates
the level of harvest several of the examined nest stands
have sustained for up to 60 years. Objectives would be to
maintain full stocking of about 60 trees per acre (fig. 6A),
40% or greater crown cover, and a mix of species including
early seral, fire-resistant trees. This prescription would
increase stem growth rates and provide conditions more
suitable for long-term site protection from fire and disease.
Some stands with an array of species could be maintained
in a steady-state condition using periodic 15- to 30-year removal entries. Others would eventually need stand regeneration to simulate the fires that kill the fire-intolerant
species and leave a few large shelterwood trees of the firetolerant species. A combination of silvicultural practices
that maintain a mix of steady-state and regeneration conditions across the landscape appears most appropriate. The
steady-state component would maintain the integrity of
current owl habitat, and the regeneration component assures continued neighborhood patchiness.
REFERENCES
Arno, S.F.; Sneck, K.M. 1977. A method for determining
fire history in coniferous forests of the mountain West.
Gen. Tech. Rep. INT-42. Ogden, UT: U.S. Department
of Agriculture, Forest Service, Intennountain Forest and
Range Experiment Station. 28 p.
Carey, A.B.; Reid, J.; Horton, S. 1990. Spotted owl home
range and habitat use in southern Oregon coast ranges.
Journal of Wildlife Management. 54: 11-17.
Thomas, J.W.; Forsman, E.D.; Lint, J.B.; Meslow, E.C.;
Noon, B.R.; Verner, J. 1990. A conservation strategy for
the northern spotted owl. Report of the Interagency Scientific Committee to address the conservation of the northern spotted owl. 427 p.
U.S. Department of Agriculture. 1983. The principal laws
relating to Forest Service activities. Agric. Handb. 453.
Washington, DC: Forest Service. 591 p.
U.S. Department of Agriculture. 1986. Interim definitions
for old-growth Douglas-fir and mixed-conifer forests in
the Pacific Northwest and California. Res. Note PNW-447.
Portland, OR: Forest Service, Pacific Northwest Research
Station.
SUMMARY
Spotted owl nest stands and neighborhoods we examined
are diverse in vegetative cover and structure. No one
39